Exemplary embodiments herein generally relate to vehicle HVAC systems, and, more particularly, relate to a partial recirculation vehicle HVAC system with ram pressure control.
It is known to provide heating, ventilation, and air conditioning (HVAC) systems in vehicles. These systems heat and cool the air within the passenger compartment for the comfort of the vehicle passengers. Some vehicle HVAC systems can be selectively configured to change the source of air. In one configuration, the HVAC system draws in fresh air from outside the vehicle, conditions the air, and then pumps the conditioned air into the passenger compartment. In another configuration, the HVAC system draws in air from inside the passenger compartment, conditions the air, and then recirculates the air into the passenger compartment. In still another configuration, the HVAC system draws in a mixture of exterior air and interior air, conditions the mixed air, and then pumps the conditioned air into the passenger compartment. In the “mixture” configuration, the passengers receive a portion of fresh air, which can reduce window fogging and also make riding in the vehicle more pleasant, and receive a portion of recirculated air, which can increase fuel economy.
Although these known vehicle HVAC systems have worked for their intended purposes, some disadvantages remain. For instance, with these HVAC systems, as vehicle speed increases the ratio between fresh air and recirculation air will change. When the vehicle is traveling at higher rates of speed, the pressure of the exterior air entering the exterior air intake of the HVAC system (i.e., the “ram air” or “ram pressure”) is relatively high. The amount of fresh air intake increases and the amount of recirculation air decreases due to the inability of the sucking pressure of the blower unit to overcome an increase in ram air pressure. As a result, the high humidity associated with the fresh air intake can significantly increase compressor load which, in turn, causes fuel economy efficiency to decrease.